Membrane filtration using low energy feed spacer

Abstract

In at least one embodiment, a membrane filtration element is provided. The element may include at least one feed spacer including a first set of parallel strands extending in a first direction and including a plurality of first strands having a first thickness and a plurality of second strands having a second thickness that is smaller than the first thickness. A second set of parallel strands may extend in a second direction that is transverse to the first direction. The second set of parallel strands may include a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness. In one embodiment, the first and second sets of strands include alternating thick and thin strands, which reduce pressure drop in membrane filtration systems.

What is claimed is: 
     
       1. A spiral wound filtration element comprising:
 a central collection tube having at least one hole defined therein; 
 at least one membrane envelope attached to the central collection tube and having two membrane sheets separated by a spacer, the at least one membrane envelope configured to be wrapped around the central collection tube to form a spiral; and 
 at least one feed spacer configured to be disposed adjacent to at least one membrane sheet of the two membrane sheets when wrapped around the central collection tube and to create a channel to receive liquid to be filtered, the at least one feed spacer configured to allow fluid flow through the at least one membrane envelope, the at least one feed spacer comprising a netting including:
 a first set of solid parallel strands extending in a first direction and including a plurality of first strands having a first thickness and the plurality of second strands having a second thickness that is smaller than the first thickness, the first and second strands spaced apart from one another with an open spacing to readily allow the fluid flow between the first and second strands; and 
 a second set of solid parallel strands integrally connected to the first and second strands extending in a second direction that is transverse to the first direction, 
 wherein the second set of parallel strands includes a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness; and 
 wherein the first set of strands and the second set of strands are always located on the same side of each other. 
 
 
     
     
       2. The spiral wound filtration element of  claim 1 , wherein the first set of parallel strands comprises alternating the first and second strands. 
     
     
       3. The spiral wound filtration element of  claim 1 , wherein the first set of parallel strands comprises alternating the first and second strands and the second set of parallel strands comprises alternating the third and fourth strands. 
     
     
       4. The spiral wound filtration element of  claim 1 , wherein the first strands and the third strands have thicknesses of 5 to 40 mils and the second strands and the fourth strands have thicknesses of 3 to 35 mils. 
     
     
       5. The spiral wound filtration element of  claim 1 , wherein the first strands and the third strands have thicknesses of 8 to 35 mils and the second strands and the fourth strands have thicknesses of 5 to 15 mils. 
     
     
       6. The spiral wound filtration element of  claim 1 , wherein the first strands and the third strands have thicknesses of 10 to 30 mils and the second strands and the fourth strands have thicknesses of 7 to 12 mils. 
     
     
       7. The spiral wound filtration element of  claim 1 , wherein the first strands and the third strands have the same thickness and the second strands and the fourth strands have the same thickness. 
     
     
       8. The spiral wound filtration element of  claim 1 , wherein the netting has a total thickness at an intersection of the first strands and the third strands of 25 to 50 mils. 
     
     
       9. The spiral wound filtration element of  claim 1 , wherein the first set of parallel strands is perpendicular to the second set of parallel strands. 
     
     
       10. The spiral wound filtration element of  claim 1 , wherein the first set of parallel strands intersects the second set of parallel strands at an angle of 65 to 110 degrees in a direction parallel to a longitudinal axis of the spiral wound filtration element. 
     
     
       11. The spiral wound filtration element of  claim 1 , wherein a pressure drop of the spiral wound filtration element is reduced by at least 10% compared to a same spiral wound filtration element having a feed spacer with strands having substantially identical thicknesses. 
     
     
       12. The spiral wound filtration element of  claim 1 , wherein the at least one feed spacer includes from 0.1 to 10% by weight of ultra-high molecular weight polyethylene. 
     
     
       13. An extruded netting comprising:
 a first set of parallel strands extending in a first direction and including a plurality of first strands having a first thickness and a plurality of second strands having a second thickness that is smaller than the first thickness; and 
 a second set of parallel strands extending in a second direction that is transverse to the first direction and including a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness; 
 wherein the first set of parallel strands and the second set of parallel strands are always located on the same side of each other; and 
 the first set of parallel strands comprises alternating the first and second strands, and the second set of parallel strands comprises alternating the third and fourth strands. 
 
     
     
       14. The extruded netting of  claim 13  further comprising from 0.1 to 10% by weight of ultra-high molecular weight polyethylene. 
     
     
       15. The extruded netting of  claim 13 , wherein the first strands and the third strands have thicknesses of 5 to 40 mils and the second strands and the fourth strands have thicknesses of 3 to 35 mils. 
     
     
       16. The extruded netting of  claim 13 , wherein the first strands and the third strands have thicknesses of 8 to 35 mils and the second strands and the fourth strands have thicknesses of 5 to 15 mils. 
     
     
       17. The extruded netting of  claim 13 , wherein the netting has a total thickness at an intersection of the first and second set of parallel strands of 25 to 50 mils. 
     
     
       18. The extruded netting of  claim 13 , wherein the netting is formed into an element having a longitudinal axis and wherein the first set of parallel strands intersects the second set of parallel strands at an angle of 65 to 110 degrees in a direction parallel to the longitudinal axis of the element. 
     
     
       19. A spiral wound filtration element comprising:
 a central collection tube having at least one hole defined therein; 
 at least one membrane envelope attached to the central collection tube and having two membrane sheets separated by a spacer, the at least one membrane envelope configured to be wrapped around the central collection tube to form a spiral; and 
 at least one feed spacer disposed adjacent to at least one membrane sheet of the two membrane sheets when wrapped around the central collection tube and to create a channel to receive liquid to be filtered, the at least one feed spacer comprising a netting including:
 a first set of parallel strands extending in a first direction and including a plurality of first strands having a first thickness and a plurality of second strands having a second thickness that is smaller than the first thickness; and 
 a second set of parallel strands extending in a second direction that is transverse to the first direction and including a plurality of third strands having a third thickness and a plurality of fourth strands having a fourth thickness that is smaller than the third thickness; 
 
 wherein the first set of parallel strands and the second set of parallel strands form opposite faces of the at least one feed spacer.